1. Field of the Invention
The present invention relates to medical monitoring systems and, in particular, to a highly portable, non-invasive, physiological data telemetry recording system for monitoring sleep disorders.
2. Discussion of the Prior Art
Conventional practice for diagnosing sleep disorders requires that the patient be admitted to a "sleep lab". Typically, these sleep labs are located at hospitals or clinics and consist of a special in-patient unit equipped with a complicated array of cumbersome polysomnograph equipment. The patient is required to sleep in the unit while being monitored by a combination of bulky, uncomfortable sensors which are attached to various parts of the body. Obviously, the accuracy of the data generated under these circumstances is suspect because of the unfamiliar environment and physically uncomfortable circumstances in which the data is taken.
To eliminate the problems associated with "sleep labs", solid-state portable physiological monitoring systems have been developed for use in the patient's own environment.
One such system is available from Vitalog Corporation. The Vitalog system is a portable microcomputer which monitors information from up to eight physiological sensors. This information is processed and stored in on-board, solid-state memory for subsequent retrieval or display by a separate computer system.
The Vitalog system contains an eight-channel analog-to-digital interface and an R-wave detector. The multichannel A/D converter samples eight analog inputs. A one-channel motion sensor composed of an array of omnidirectional mercury tilt switches detects patient movement. A one-channel electrocardiogram (ECG) signal is monitored using three standard ECG electrode pads. The amplified ECG signal is connected to an A/D channel and also to the R-wave detection circuit. A temperature sensor array monitors three channels of temperature using standard probes. Either one or two channels of respiration may be monitored. One channel can be programmed to monitor a patient response button.
When the Vitalog system is activated, its ROM-based operating system continuously monitors the sensor inputs. After each programmed monitoring period, information relating to heart rate, physical activity and temperature is stored. A running mean of normal R-R intervals is calculated at the end of each heart beat. At the end of each monitoring period, the current mean is encoded into one of 16 levels (4 bits) and stored. A filtered output count from the motion sensor is accumulated and encoded into one of 8 levels (3 bits). Temperature information is encoded using a 3-bit tracking scheme.
The Vitalog system can store data from a minimum of 3600 epochs. Data compression is used to ensure that no memory is used when data is unchanging.
A fundamental shortcoming of the Vitalog system is that it lacks individual event resolution. That is, because data gathered over a full monitoring period must be stored in limited on-board memory for retrieval at the end of the monitoring period, the data must be compressed prior to storage. This requires pre-storage processing according to a predefined algorithm, further limiting the stored data characteristics to rigid identifying and modifying signatures, thus reducing analytical flexibility.
Thus, while the Vitalog system provides a screening tool, it does not address the need for a low cost, reliable, portable physiological data recording system which provides high data resolution for a number of parameters over long periods of time.